triedb/pathdb: improve pruner

triedb/pathdb/history_index_pruner.go

@@ -220,13 +220,6 @@ func (p *indexPruner) prunePrefix(prefix []byte, elemType elementType, tail uint
 			it.Release()
 			break
 		}
-		// Periodically release the iterator so the LSM compactor
-		// is not blocked by the read snapshot we hold.
-		if time.Since(opened) >= iteratorReopenInterval {
-			start := common.CopyBytes(it.Key()[len(prefix):])
-			it.Release()
-			it = p.disk.NewIterator(prefix, start)
-		}
 		// Check termination or pause request
 		select {
 		case <-p.closed:
@@ -240,26 +233,35 @@ func (p *indexPruner) prunePrefix(prefix []byte, elemType elementType, tail uint
 		case ack := <-p.pauseReq:
 			// Save the current position so that after resume the
 			// iterator can be re-opened from where it left off.
-			key := it.Key()
-			start := common.CopyBytes(key[len(prefix):])
+			start := common.CopyBytes(it.Key()[len(prefix):])
 			it.Release()
 
 			// Flush all pending writes before acknowledging the pause.
+			var flushErr error
 			if batch.ValueSize() > 0 {
 				if err := batch.Write(); err != nil {
-					close(ack)
-					return 0, err
+					flushErr = err
 				}
 				batch.Reset()
 			}
 			close(ack)
 
-			// Block until resumed or closed
+			// Block until resumed or closed. Always wait here even if
+			// the flush failed — returning early would cause resume()
+			// to deadlock since nobody would receive on resumeCh.
 			select {
 			case <-p.resumeCh:
+				if flushErr != nil {
+					return 0, flushErr
+				}
+				// Re-open the iterator from the saved position so the
+				// pruner sees the current database state (including any
+				// writes made by indexer during the pause).
 				it = p.disk.NewIterator(prefix, start)
+				opened = time.Now()
+				continue
 			case <-p.closed:
-				return pruned, nil
+				return pruned, flushErr
 			}
 
 		default:
@@ -284,6 +286,16 @@ func (p *indexPruner) prunePrefix(prefix []byte, elemType elementType, tail uint
 			}
 			batch.Reset()
 		}
+
+		// Periodically release the iterator so the LSM compactor
+		// is not blocked by the read snapshot we hold.
+		if time.Since(opened) >= iteratorReopenInterval {
+			opened = time.Now()
+
+			start := common.CopyBytes(it.Key()[len(prefix):])
+			it.Release()
+			it = p.disk.NewIterator(prefix, start)
+		}
 	}
 	if batch.ValueSize() > 0 {
 		if err := batch.Write(); err != nil {